The present invention relates to methods of enhancing the conductivity of propped fractures with in-situ acidizing.
Subterranean wells (e.g., hydrocarbon producing wells, water producing wells, and injection wells) are often stimulated by hydraulic fracturing treatments. In traditional hydraulic fracturing treatments, a viscous treatment fluid is pumped into a portion of a subterranean formation at a rate and pressure such that the subterranean formation breaks down and one or more fractures are formed. While the treatment fluid used to initiate the fracture is generally solids-free, typically, particulate solids, such as graded sand, are suspended in a later portion of the treatment fluid and then deposited into the fractures. These particulate solids, or “proppant particulates,” serve to prop the fracture open (e.g., keep the fracture from fully closing) after the hydraulic pressure is removed. By keeping the fracture from fully closing, the proppants aid in forming conductive paths through which produced fluids, such as hydrocarbons, may flow.
The degree of success of a fracturing operation depends, at least in part, upon fracture conductivity once the fracturing operation is complete and production is begun. Traditional fracturing operations place a large volume of proppant particulates suspended in a treatment fluid into a fracture to form a “proppant pack” in order to ensure that the fracture does not close completely upon removing the hydraulic pressure. The ability of proppant particulates to maintain a fracture open depends upon the ability of the proppant particulates to withstand fracture closure and, therefore, is typically proportional to the volume of proppant particulates placed within the fracture forming the proppant pack.
In some subterranean treatment operations, traditional fracturing operations may be supplemented with enhanced oil recovery techniques. Such enhanced oil recovery techniques may operate to enhance the conductivity of fractures propped with proppant particulates. One such technique is acidizing a fracture. Acidizing involves injecting an acid (e.g., hydrochloric acid) into a fracture in a subterranean formation in order to etch channels or create microfractures in the face of the fracture in order to enhance the conductivity of the fracture. The acid may create a dendritic-like network of channels or microfractures through which treatment fluids and produced fluids may flow.
Acidizing a fracture in a subterranean formation, particularly in combination with propping the fracture, may operate to supplement or enhance the fractures conductivity and the overall production of the formation. However, acidizing may be limited due to acid spending or leakoff. If the acid is spent or experiences leakoff prior to reaching the desired interval of the subterranean formation (e.g., the fracture), it is insufficiently potent to etch channels or microfractures in the fracture and, thus, does not contribute to or only minimally contributes to enhancing the conductivity of the fracture. Additionally, acidizing may pose a threat to both subterranean formation equipment and operators during well stimulation operations. Subterranean formation operation equipment may be corroded by the acidizing techniques, which involve the placement of strong acids into, for example, steel or iron equipment (e.g., transport, storage, and pumping equipment). Often, corrosion inhibitors are used to combat the effects of acid exposure during acidizing techniques, but they may not be fully effective and may be rather expensive and, thus, cost prohibitive. In addition, handling of acids poses great threat to operators during subterranean formation stimulation operations. Therefore, a method of acidizing a propped fracture at the target interval within a subterranean formation may be of benefit to one of ordinary skill in the art.